mechanochemical treatmentotherwise mechanical milling and alloying
(rus. механохимическое воздействие)
— mechanical treatment which leads to grinding and a plastic deformation of solid mixtures or the substances, acceleration of a mass transfer, components mixing at the atomic level and activation of chemical interaction between solid reagents.

Description

Mechanochemical treatment as a method of high energy mechanical treatment of a solid body can be divided into two main types: mechanical milling (or ball milling), and mechanical alloying (or mechanochemical synthesis). In both cases, various designs of planetary and jet mills, or disintegrators are used.

Pulverisation caused by shock, shock-abrasive or abrasive action leads to the accumulation of structural defects in solid particles, phase transformations and even the amorphisation of crystals, which affects their chemical activity. Mechanical activation occurs when the rate of defect accumulation exceeds the rate of their disappearance.

Mechanical alloying provides mass transfer and chemical interaction in powders of pure elements, compounds or alloys. Mechanical alloying makes it possible to obtain substances in either a crystalline or an amorphous state. In addition, mechanical alloying makes it possible to achieve complete mutual solid-state solubility of such elements, whose mutual solubility at equilibrium conditions is negligible.

Mechanical grinding is one of the most efficient methods for producing large amounts of nanopowders of various materials, such as metals, alloys, intermetallics, ceramics and composites.

The powders obtained by mechanochemical synthesis have an average particle size from 200 to 5-10 nm. For example, mechanochemical synthesis of TiC, ZrC, VC and NbC carbide nanopowders by milling a mixture of metal and carbon powders in a ball mill leads to the formation of carbides after 4-12 hours of milling, and the size of carbide particles after 48 hours of milling is 7 ± 1 nm.

Illustrations

Original powder mix of titanium and graphite (a) and very large (up to 1 mm) composite (Ti + C) particles of the powder mix after three hours of milling in a drum mill (b). Titanium carbide starts developing after 4 hours of milling; eleven hours after the milling has begun, 5-8 um agglomerates start appearing from TiC grains sized 10-100 nm (c); after 200 hours of milling, TiC grains have the size of 2-3 nm and are agglomerated into particles sized 300-400 nm (d).